We will continue to study the origin, circulation and fate of membranes and membrane-delimited organelles in neurons and other cells of the nervous system, using electron microscope cytochemistry combined with physiological determinations. One principal focus of the proposed research will be on the involvement of the agranular endoplasmic reticulum in these processes. We will follow up leads suggesting that distinctive regions of the reticulum may particpate, along with other organelles such as the Golgi apparatus, in the origin of different structures such as synaptic vesicles, membranes of retinal photoreceptor outer segments, and lysosomes. We will also continue our study of endocytic membrane retrieval processes and related retrograde transport: 1) exploring alternatives to horseradish peroxidase for studying such processes; 2) examining aspects of the fate of endocytically derived structures formed in presynaptic terminals; 3) containuing our use of endocytic tracer approaches as a means to supplement physiological and biochemical methods for monitoring levels of synaptic activity in the isolated frog retina under varying physiological and experimental conditions. Another methodological interest we will pursue is the use of immunohistochemical procedures for studying membrane-associated proteins; with such techniques we will do further work on the acetylcholine receptor. Finally, we will continue our investigations of peroxisomes of neurons and glia, especially our efforts to delineate their enzymatic capacities and to determine their roles.